We have hitherto spoken only of lime, and of carbonate of lime: is lime found native in any other state of combination?

Lime exists in large quantities in various parts of the earth combined with sulphuric acid, which forms gypsum*; with the fluoric acid in the fluor spart; with the phosphoric acid in a mineral called apatite‡, and in some precious stones.

What is magnesia?

Magnesia is a very soft, white, light earth: with little taste or smells; unalterable in the fire ||, and almost insoluble in water.¶ With sulphuric acid it forms a salt very easy of solution**. How is magnesia procured?

Magnesia is not found in a state of purity, but is generally procured from sulphate of magnesia (Epsom salt++) which exists

in which I shall endeavour to explain the different operations on chymical principles, and how each process may be conducted to the best advantage. We have no English work on soap-making, and I believe there is nothing in any language worth reading on this subject except the "Report on the Fabrication of Soaps, made by Darcet, Lelievre, and Pelletier, by order of the committee of Public Safety," in the 19th volume of the Ann. de Chimie; but as the French make use of articles which our soap-makers cannot avail themselves of, a great part even of that paper is not applicable to the practice in this country.

* Gypsum is composed of 30 parts of sulphuric acid, 32 earth, and 38 water. Kirwan.

Lime combined with the fluoric acid forms those beautiful fluor spare which are brought from the mines of Derbyshire. Combined with muriatic acid, large quantities of this earth are held in solution by the waters of the

ocean.

The bones of all kinds of animals are formed of this earth and phosphoric acid, in the proportion of about 80 parts earth and 20 parts acid. The best test for the presence of lime is oxalic acid, which forms with it an insoluble precipitate. Oxalate of ammonia is generally used for this

purpose.

Magnesia converts vegetable blues to a green. In this respect it resembles the alkalies. Indeed some chymical writers have classed it with

the alkalies.

Though this earth is infusible of itself, it assists the fusion of every other body. It requires near 8000 times its weight of water to hold it in solution : nothwithstanding this, it has the property of rendering camphor, opium, and resins, soluble in water. Its specific gravity is 2.33.

¶ Magnesia dissolves in alkaline carbonates, but is not soluble in the caustic alkalies.

** Sulphate of magnesia is found in several mineral waters. The bitter saline waters generally owe their taste to this salt. All the salts formed with this earth are bitter, and generally very soluble.

The Epsom salt (sulphate of magnesia) of commerce is generally procured from the mothers which remain after the separation of common salt from sea water, by adding thereto sulphate of iron. In this process the phuric acid leaves the iron to unite with the magnesia, and the muriatic which was before combined with it unites with the iron.

The magnesia used in medicine is prepared thus: A solution of carbo

in abundance in sea-water, and in many springs*.

What are the uses of magnesia?

Magnesia, in a separate state, has important uses in medicine+. It is useful also in some chymical processes; and is employed by the manufacturers of enamels and porcelain. It is also the most effectual antidote in case of poison by the mineral acids‡..

Are there not instances in nature of the earths entering into combination with each other§?

Yes minerals are found in which the earths are combined in different proportions by processes unknown to us, and which Nature employs to produce the variety of texture, transparency, colour, &c. visible in them.

nate of potash, or soda, is poured into a heated solution of sulphate of magnesia, when a double decomposition and combination take place. The sulphuric acid of the sulphate of magnesia seizes the alkali, and the carbonic acid of the alkali combines with the magnesia. Thus carbonate of magnesia and sulphate of alkali result from the process.

Muriate of magnesia is also found in sea water. Inverary-House is Built with a stone called lapis ollaris, which contains a large portion of magnesia.

Magnesia is found in talc, steatites, potstone, asbestus, fossil cork, and other minerals. The stones which contain a large portion of this earth have generally an unctuous feel, a fibrous texture, and a silky lustre

When magnesia is taken as an aperient, it ought to be in the state of carbonate of magnesia, or what is called mild magnesia. When it is taken as an absorbent to correct acidities, calcined or caustic magnesia is most proper. On several accounts it is of consequence to attend to this distinction.

If putrid water be agitated with a small quantity of magnesia, it will lose its bad taste and smell in a few minutes. Proust, Journal de Physique. Might not this method be of use sometimes at sea, on long voyages?

Alumine and silex are the earths which have the greatest affinity. These earths are found in nature oftener united than any other. The hardest stones are formed of these two earths.

Monsieur Guyton de Morveau has proved by direct experiment that the earths have not only an affinity for each other capable of producing combina tion, but likewise an elective attraction, which destroys one compound in order to form another. The paper containing an account of his experiments may be seen in Annales de Chimie, tom. xxxi.

Mr. Chenevix's memoir on this subject, in the Phil. Trans. for 1802, is also very interesting.

Potter's clay is a mixture chiefly of silex and alumine; the colouring earths used as pigments are mixtures either of clay and the oxides of iron, or clay and charcoal; garden mould is a mixture extremely various, sometimes containing silex, alumine, magnesia, iron, lime, and carbon; the common millstone is generally composed of alumme and silex, whereas the crumbling sandstope is a mixture of iron and silex.

But it is impossible to enumerate the endless diversity of substances which Nature offers ready formed for the use of man; for the mixtures of the earths which are found naturally combined, comprehend all the varieties of clays, slates, stones, spars, gems, rocks, crystals, zeolites, quartz, flints, &c.

A regular classification of the different earths and stones, according to

What do you suppose could be the design of Nature in forming so distinct earths?

many

The earths have several properties in common; yet as every earth possesses different and specific properties, it is evident that Nature designed them for different and distinct purposes of utility.

You have enumerated the separate uses of most of the earths, can you recollect the collective advantages which arise from this class of

bodies?

The uses of zircone, glucine, yttria, and strontian are not yet known; but the benefits which we derive from the other earths are too various and important to be enumerated. Besides that they afford support to the vegetable creation, they possess so many valuable properties, that man may attain a very high degree of civilization and comfort by their means.

In order to impress your memory, and to finish the consideration of this class of bodies, endeavour to recollect those uses of the earths which appear to you to be most important.

LIME, then, has an extensive and important use in agriculture*; it is employed in building, &c. and adds much both to the neatness and durability of our dwellings. SILEX is the basis of all mortars and cements, and is a necessary ingredient in earthen ware, porcelain, and glass. BARYTES is employed in chymical laboratories as a re-agent, and for the formation of salts. MAGNESIA, besides being the basis of several salts, is of great use in medicine; and ALUMINE, by its mixture with silex, forms vessels for chymists capable of resisting the action of the most concentrated acids; is the material of which the bricks are formed which construct the walls of our habitations, and is spread out by the great Author of nature in strata within our hills and mountains, to arrest the progress of subterraneous waters, and

the system of M. Daubenton, may be seen in the first volume of Thomson's Fourcroy..

A few short directions for analysing stones are given in Parkinson's Chymical Pocket-book. There is an excellent paper on this subject in vol. iv. of Dr. Thomson's System of Chymistry. Fourcroy's directions are more concise, but they are worth the perusal of those who are not accustomed to this kind of analysis. Further information may be had by consulting Kirwan's Mineralogy, vol. i.

The minerals which are generally the subject of analysis with chymists are formed with different proportions of the nine earths and the metallic oxides; such as oxide of iron, copper, nickel, manganese, crome, &c.

*The goodness of a soil depends upon its being able to retain the quantity of moisture which is proper for the nourishment of vegetables, and no more. Now the retentive power of a soil increases with the proportion of its alumine, lime, or magnesia; and diminishes as the proportion of its silex increases." Dr. Thomson.

Some have imagined that the earth would have had more beauty, and

to produce those springs that fertilize the valleys, and which take such diversified courses upon the surface of the globe.

would have been much more convenient, if the whole had been a plane surface; and others have gone so far as to adduce the mountainous parts of the world as a proof of the imperfection of the works of Nature; but, independent of the beautiful variety which they give to the surface of the globe, they are the sole cause of all our springs, and the origin of rivers, without which we have a difficulty in conceiving how animal and vegetable life could have been preserved.

Like the good man who, elevated by his rank, virtues, and talents, stands erect in conscious integrity, and dispenses blessings of every kind around him-they raise their towering heads towards heaven, to draw from thence the fructifying waters; and when purified by suffering them to percolate though their siliceous beds, they pour them forth in a thousand streams to fertilize and bless every region of the earth.

When we consider that the crystal spring and the meandering_river owe their origin entirely to these eminences dispersed over the earth's surface, what importance do they acquire in our estimation! and what reason have we to admire the wisdom of that Being who had an eye to every exigency, and in the infinity of his power has amply provided for them all!

CHAPTER VI.

OF ALKALIES..

WHAT is the nature* of an alkali?

The alkaliest have an acrid and urinous taste; they change the blue juices of vegetables to a green; and have the property of rendering oils miscible with water. They are incombustible, but may be rendered volatile by a great heat. They are soluble in water: form various salts by combination with acids‡; and act as powerful caustics § when applied to the flesh of animals [].

No written description that can be given of an alkali will convey any correct idea of the taste or properties of this class of bodies to a person who has had no opportunity of examining an alkali: let the pupil therefore procure a specimen of each kind before he enters upon this chapter. The juice of the gooseberry and the lemon, and many other vegetable substances will remind him of the general properties of the acids; but having met with nothing analogous to the alkalies, it will be necessary for him to taste and examine one of these bodies in order to acquire any thing like a just idea of their nature. Let him form potash or soda into a neutral salt by saturating it with one of the acids, and he will perceive still more of the nature of these bodies.

+ The word alkali is of Arabian origin, and signifies the " bitterness." Dr. Thomson.

dregs of

↑ Potash becomes mild by its union with carbonic acid; the most caustic 'soda, if united to corrosive muriatic acid, forms the mild salt used at our tables.

It seems that causticity depends on chymical affinity, and that the caustic substance corrodes the matter to which it is applied, in consequence of its tendency to unite with that matter; and that it continues to act upon it until it has saturated itself by the combination. Thus the most caustic alkalies may be combined so as to form insipid salts. See Macquer's Chy. mical Dictionary, where this chymical operation is very fully explained.

If a piece of animal flesh be put into a strong solution of potash or soda, it will immediately be acted upon by the alkali, and will soon be entirely dissolved thereby, so that the whole will appear as one mass.

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